Phosphor placement in white light emitting diode assemblies

ABSTRACT

A white LED assembly includes a blue LED die attached to a substrate. A first volume of a first luminescent material surrounds the blue LED die in a lateral dimension such that none of the first luminescent material is disposed directly over the blue LED die. The first luminescent material includes a relatively inefficient phosphor having a peak emission wavelength longer than 620 nm and includes substantially no phosphor having a peak emission wavelength shorter than 620 nm. A second volume of a second luminescent material is disposed over the first volume and the blue LED die. The second luminescent material includes a relatively efficient phosphor having a peak emission wavelength shorter than 620 nm and includes substantially no phosphor having a peak emission wavelength longer than 620 nm. Placement of the first and second luminescent materials in this way promotes removal of heat from the inefficient phosphor and reduces the likelihood of interabsorption.

TECHNICAL FIELD

The present disclosure relates generally to white LED (Light EmittingDiode) assemblies.

BACKGROUND INFORMATION

A so-called white Light Emitting Diode (LED) is a solid state devicethat converts electrical energy into light. FIG. 1 (Prior Art) is asimplified cross-sectional diagram of a white LED assembly 1. The whiteLED assembly is actually an assembly that includes a blue light emittingdiode (LED) die 2, commonly referred to as a blue LED. The active region3 within the blue LED die is an InGaN/GaN Multiple Quantum Well (MQW)structure. The blue LED die therefore emits relatively narrowband bluelight having a wavelength in a range from 455 nanometers (nm) to about455 nm. Blue LED die 2 is mounted in a reflector cup of a substrate 4.In addition to blue LED die 2 and substrate 4, the white LED assembly 1includes an amount of luminescent material 5. Luminescent material 5includes phosphor particles and a transparent binding material. Theluminescent material may be generally referred to as “phosphor”, eventhough more accurately it includes the binding material and phosphorparticles. In the example illustrated in FIG. 1, luminescent material 5includes a mixture of three types of phosphor particles suspended in atransparent silicone binding material.

A solid black dot symbol represents a red-emitting phosphor particle. Aparticular red-emitting phosphor particle may, for example, absorb bluelight emitted form the LED die. The blue light has a wavelength of 455nm. The red-emitting phosphor particle then re-emits some of theabsorbed energy as red light. The emission spectrum of the re-emittedlight is centered at a peak wavelength of about 650 nm.

A small dot symbol having a white center represents anorange/yellow-light emitting phosphor particle. A particularyellow/orange-emitting phosphor particle may, for example, absorb 455 nmblue light from the blue LED die, and then re-emit some of the absorbedenergy as yellow/orange light. The emission spectrum of the re-emittedlight is centered at a peak wavelength of about 574 nm.

A small “x” symbol represents a green-emitting phosphor particle. Aparticular green-emitting phosphor particle may, for example, absorb 455nm blue light from the blue LED die, and can then re-emit some of theabsorbed energy as green light. The emission spectrum of the re-emittedlight is centered at a peak wavelength of about 545 nm.

Some of the blue light emitted by blue LED die 2 passes all the waythrough the fluorescent material 5 without being absorbed by anyphosphor particle and exits the LED device 1 as blue light. Anotherportion of the blue light emitted by the blue LED die is absorbed byred-emitting phosphor particles such that the red-emitting phosphorparticles emit red light that in turn exits the LED device. Anotherportion of the blue light emitted by the blue LED die is absorbed byyellow/orange-emitting phosphor particles such that theyellow/orange-emitting particles emit yellow/orange light that in turnexits the LED device. Another portion of the blue light emitted by theblue LED die is absorbed by green-emitting phosphor particles such thatthe green-emitting particles emit green light that in turn exits the LEDdevice. The relative amounts, types, and relative positioning of thethree different phosphors within the LED device structure is such thatthe color spectrum of the combined light that exits the LED deviceappears to the human eye as being “white”. The LED device is thereforecommonly referred to as a “white LED”.

FIG. 2 (Prior Art) is a simplified cross-sectional diagram of a part ofwhite LED device 1. Each arrow in the diagram represents the path of aphoton. The photon represented by arrow 6 is blue light that passesthrough the fluorescent material 5 and exits the LED device as bluelight. The photon represented by arrow 7 is blue light that is absorbedby a red-emitting phosphor particle, that in turn emits a red lightphoton 8 that exists the LED device. The photon represented by arrow 9is blue light that is absorbed by a yellow/orange-emitting phosphorparticle, that in turn emits yellow/orange light 10 that exits the LEDdevice. The photon represented by arrow 11 is blue light that isabsorbed by a green-emitting phosphor particle, that in turn emits greenlight 12 that exits the LED device.

A phenomenon referred to as “interabsorption” can also occur. A phosphorparticle can absorb light emitted from another phosphor particle. Forexample, a blue light photon represented by arrow 13 is absorbed by agreen-emitting phosphor particle. The green-emitting phosphor particlethen re-emits green light represented by arrow 14. Rather than exitingthe LED assembly, the green light is absorbed by a red-emitting phosphorparticle. The red-emitting phosphor particle then re-emits red light 15.Similarly, arrow 16 represents a blue light photon that is absorbed by ayellow/orange-emitting phosphor particle. The yellow/orange-emittingphosphor particle then re-emits yellow-orange light 17. Rather than theyellow/orange light exiting 17 the LED device, the yellow/orange light17 is absorbed by a red-emitting phosphor particle, that in turn emitsred light 18. Although not illustrated, other complex interabsorptionevents can occur. For example, light emitted from an excitedgreen-emitting phosphor particle may be absorbed by absorbed by ayellow/orange-emitting phosphor particle.

FIGS. 3-6 (Prior Art) are diagrams of LED assemblies set forth in U.S.Pat. No. 7,250,714. In the LED assembly 19 of FIG. 3, the red-emittingphosphor 20 and the green/yellow-emitting phosphor 21 are depositedadjacent to each other with respect to blue LED die 22 such thatabsorption by the red-emitting phosphor of light emitted by thegreen/yellow emitting phosphor is reduced. In the LED assembly 23 ofFIG. 4, the green/yellow-emitting phosphor 24 and the red-emittingphosphor 25 are deposited over LED die 26 as discrete layers, with thered-emitting phosphor layer 25 deposited closest to the LED 26. Thegreen/yellow emitting-phosphor layer and the red-emitting phosphorlayers may be separated by an optional transparent layer 27. In the LEDassembly 28 of FIG. 5, the green/yellow-emitting phosphor 29 and theother phosphors 30 are deposited in a plurality of small regions on ablue LED die 31 as illustrated. In the LED assembly 32 of FIG. 6, smallregions 33 of red-emitting phosphor are formed on the surface of a blueLED die 34. A layer of green/yellow-emitting phosphor 35 is depositedover the plurality of regions 33 as illustrated. In each of the LEDassemblies of FIGS. 3-6, the arrangements of the yellow/orange-emittingphosphor and the red-emitting phosphor reduce the probability that lightemitted from the green/yellow-emitting phosphor will be absorbed by thered-emitting phosphor. See U.S. Pat. No. 7,250,714 for further details.

SUMMARY

A white LED assembly includes a blue LED die attached to a substrate.The blue LED die may, for example, be either a laterally-contacted blueLED die or a vertically-contacted blue LED die. The blue LED die iscapable of emitting blue light. The blue LED defines a Right RectangularPrism (RRP) whose base face is the bottom of side of the die. A firstperipheral side of the die lies in a first plane that is coplanar with afirst side face of the RRP. A second peripheral side of the die lies ina second plane that is coplanar with a second side face of the RRP. Athird peripheral side of the die lies in a third plane that is coplanarwith a third side face of the RRP. A fourth peripheral side of the dielies in a fourth plane that is coplanar with a fourth side face of theRRP.

The white LED assembly further includes a first volume of a firstluminescent material that is formed to surround the blue LED die in alateral dimension such that the first luminescent material is in contactwith the substrate and such that substantially none of the firstluminescent material is disposed directly over the blue LED die. Thefirst volume is formed such that the first volume is disposed entirelyoutside the RRP.

The first luminescent material comprises a first phosphor material and atransparent binding material such as silicone. The first phosphormaterial is capable of absorbing blue light from the blue LED die andemitting light having a first peak wavelength longer than 620 nm. Thefirst luminescent material comprises substantially no phosphor materialcapable of emitting light having a peak wavelength shorter thanapproximately 620 nm. The first phosphor material may be red-emittingphosphor particles.

The white LED assembly further includes a second volume of a secondluminescent material that is formed such that the second volume isdisposed at least in part above the die within the RRP. The secondluminescent material comprises a second phosphor material and atransparent material such as silicone. The second phosphor material iscapable of absorbing blue light from the blue LED die and emitting lighthaving a second peak wavelength shorter than 620 nm. The secondluminescent material comprises substantially no phosphor materialcapable of emitting light having a peak wavelength longer thanapproximately 620 nm. The second phosphor material may be a mixture ofyellow/orange-emitting phosphor particles and green-emitting particles.

The first phosphor material has a relatively low conversion efficiencyas compared to the conversion efficiency of the second phosphormaterial. Placement of the first and second luminescent materials in thewhite LED assembly promotes removal of heat from the inefficient firstphosphor material and reduces the likelihood of interabsorption.

Further details and embodiments and methods are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 (Prior Art) is a simplified cross-sectional diagram of a whiteLED assembly.

FIG. 2 (Prior Art) is a simplified cross-sectional diagram of a part ofthe white LED device of FIG. 1.

FIGS. 3-6 (Prior Art) are diagrams of various LED assemblies set forthin U.S. Pat. No. 7,250,714.

FIG. 7 is a simplified perspective diagram of a white LED assembly inaccordance with one novel aspect.

FIG. 8 is a simplified cross-sectional diagram of the white LED assemblyof FIG. 7 taken along sectional line A-A.

FIG. 9 is a cross-sectional diagram that identifies a section ofstructure of FIG. 8.

FIG. 10 is an expanded perspective view of the section identified inFIG. 9.

FIG. 11 is a cross-sectional view of the section of FIG. 10.

FIG. 12 is a simplified top-down diagram of the section of FIG. 10.

FIG. 13 is a diagram that shows the ranges of wavelengths that areconsidered to be red light, orange light, yellow light, and green light,in one example.

FIG. 14 is a table that illustrates an exemplary system of phosphors forthe white LED assembly of FIG. 7.

FIG. 15 is a diagram that illustrates operational aspects of the whiteLED assembly of FIG. 7.

FIG. 16 is a cross-sectional side view of a second white LED assembly inaccordance with another novel aspect.

FIG. 17 is a cross-sectional side view of a third white LED assembly inaccordance with another novel aspect.

FIG. 18 is a cross-sectional side view of a fourth white LED assembly inaccordance with another novel aspect.

FIG. 19 is a cross-sectional side view of a fifth white LED assembly inaccordance with another novel aspect.

FIG. 20 is a cross-sectional side view of a sixth white LED assembly inaccordance with another novel aspect.

FIG. 21 is a cross-sectional side view of a seventh white LED assemblyin accordance with another novel aspect.

FIG. 22 is a cross-sectional side view of an eighth white LED assemblyin accordance with another novel aspect.

FIG. 23 is a flowchart of a method in accordance with one novel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. In the description and claims below, when a first object isreferred to as being disposed “on” a second object, it is to beunderstood that the first object can be directly on the second object,or an intervening object may be present between the first and secondobjects. Similarly, terms such as “above”, “beneath”, “lateral”,“vertical”, upper”, and “lower” are used herein to describe relativeorientations between different parts of the white LED assembly structurebeing described, and it is to be understood that the overall white LEDassembly being described can actually be oriented in any way inthree-dimensional space.

FIG. 7 is a simplified perspective diagram of a white LED assembly 50 inaccordance with one novel aspect. A molded two-dimensional array 51 ofdome-shaped mini-lens structures is disposed on a square substrate 52.Reference numerals 53-56 identify four of these dome-shaped mini-lensstructures.

FIG. 8 is a simplified cross-sectional diagram of the white LED assembly50 taken along sectional line A-A of FIG. 7. Blue LED dice 57-60 areattached to the upper surface 61 of substrate 52 as illustrated. Theblue LED dice 57-60 have InGaN/GaN Multiple Quantum Well (MQW) activeregions and therefore emit relatively narrowband blue light having awavelength in a range from 455 nanometers (nm) to about 455 nm. Detailssuch as the contour of the upper surface of substrate 52, variouscontact terminals, conductive layers, insulative layer, solder masklayers, highly reflective coating layers, and wire bonds are omittedfrom the diagram in order not to obscure other parts of the diagram andto simplify the corresponding description. In the illustrated example, aperipheral square retaining ring 62 is provided around thetwo-dimensional array of dice. Peripheral retaining ring 62 may, forexample, be a pre-molded silicone object that after pre-molding andcuring is attached to the upper surface of substrate 52. In otherexamples, an amount of uncured silicone or another curable material isplaced onto the substrate and is allowed to cure in place to form thestructure of the retaining ring.

A first volume 63 of a first luminescent material is formed so thatvolume 63 surrounds each of the dice in the lateral dimension. Firstluminescent material includes powder particles of a first phosphormaterial. The particles of the first phosphor material are suspended ina transparent binding material. In the illustrated example, the bindingmaterial is silicone. In the illustrated example, the first phosphormaterial is a red-emitting phosphor material. In FIG. 8, the small blacksolid dot symbols represent red-emitting phosphor particles.

In one specific example, the red-emitting phosphor is an Europium-dopednitride-based phosphor described by the approximate formulaCaAlSiN₃:Eu²⁺. The red-emitting phosphor has an absorption spectrum suchthat the red-emitting phosphor absorbs relatively narrowband blue lightemitted from the blue LED dice. The red-emitting phosphor has anemission spectrum such that the red-emitting phosphor emits relativelybroadband red light having a peak wavelength of 650 nm.

The upper surface of first volume 63 lies in a plane that is roughlycolinear with planar upper surface portions of the dice 57-60 asillustrated in FIG. 8. In some examples the blue LED dice arelaterally-contacted blue LED dice, whereas in other examples the blueLED dice are vertically-contacted blue LED dice. Regardless of the typeof blue LED die used, a portion of the upper surface of each die issubstantially planar. The upper surface of first volume 63 may beslightly above the plane of these upper planar surface portions, or theupper surface of the first volume 63 may be coplanar with the plane ofthese upper planar surface portions, or the upper surface of the firstvolume 63 may be slightly below the plane of these upper planar surfaceportions. The upper surface of first volume 63 may be smooth, or mayhave a roughened surface to promote the escape of light from the LEDdice upward and out of first volume 63.

In some cases, the first luminescent material is jetted onto the uppersurface of substrate 52 in the form of microdots of liquid uncuredphosphor-bearing silicone. In this way, the volume surrounding the diceis filled up to the approximate level of the top of the retaining ring62. The first luminescent material of the first volume contacts theupper surface of the substrate and also contacts the side edges of eachof the dice. Alternatively, the first luminescent material is put inplace using a screen printing process and is allowed to cure in place.Regardless of how the first volume is filled with the first luminescentmaterial, substantially no red phosphor is disposed directly above anypart of any of the blue LED dice.

A second volume 64 of a second luminescent material has an upper surfacethat forms the molded array 51 of dome-shaped mini-lenses. The secondluminescent material includes powder particles of a second phosphormaterial that are suspended in a transparent binding material. In theillustrated example, the binding material is silicone. In theillustrated example, the second phosphor material is a mixture ofparticles of a yellow/orange-emitting phosphor and particles of agreen-emitting phosphor. In FIG. 8, the dot symbols having white centersrepresent yellow/orange-emitting phosphor particles, whereas the small“x” symbols represent green-emitting phosphor particles.

There is one dome-shaped structure disposed and centered above eachcorresponding one of the blue LED dice. The upper surface structure ofthe second volume may be smooth, or may have a roughened contour topromote the escape of light. The maximum distance from trough to peak ofthe surface-roughening contours of the upper surface of second volume 64is in a range from one micron to one millimeter.

In one specific example, the yellow/orange-emitting phosphor is anEuropium-doped silicate-based phosphor described by the approximateformula A₃Si(OD)₄:Eu²⁺ and/or A₃Si(OD)₅:Eu²⁺, where A is a bivalent (2+)ion of Sr, Ba, or Ca, and where D is a monovalent (1−) ion of Cl, F, Nor S. The yellow/orange-emitting phosphor has an absorption spectrumsuch that the red-emitting phosphor absorbs relatively narrowband bluelight emitted from the blue LED dice. The yellow/orange-emittingphosphor has an emission spectrum such that the yellow/orange-emittingphosphor emits relatively broadband yellow/orange light having a peakwavelength of 574 nm.

In one specific example, the green-emitting phosphor is anEuropium-doped aluminate-based phosphor described by the approximateformula M_(1-x)Eu_(x)Al_(y)O_([1-3Y/2]), where M is a bivalent (2+) ionof Sr, Ba or Ca. The green-emitting phosphor has an absorption spectrumsuch that the green-emitting phosphor absorbs relatively narrowband bluelight emitted from the blue LED dice. The green-emitting phosphor has anemission spectrum such that the green-emitting phosphor emits relativelybroadband green light having a peak wavelength of 545 nm.

FIG. 9 is a cross-sectional diagram of white LED assembly 50 similar tothe view of FIG. 8, except that a section of structure is identifiedwith vertical dashed lines 65.

FIG. 10 is an expanded perspective view of the section identified inFIG. 9. A right rectangular prism (RRP) 66 extends up from theperipheral edges of the square blue LED die 58. The bottom squaresurface of die 58 is the base side of prism 66. The prism 66 has asquare cross-section when considered from a top-down perspective. Theprism 66 has four side faces 67-70. First side face 67 lies in a plane71 (see FIG. 12) that is substantially coplanar with the plane of afirst peripheral side 72 of die 58. Second side face 68 lies in a plane73 (see FIG. 12) that is substantially coplanar with the plane of asecond peripheral side 74 of die 58. Third side face 69 lies in a plane75 (see FIG. 12) that is substantially coplanar with the plane of athird peripheral side 76 of die 58. Fourth side face 70 lies in a plane77 (see FIG. 12) that is substantially coplanar with the plane of afourth peripheral side 78 of die 58. The upwardly bulging upper surfaceof second volume 64 as illustrated in FIG. 10 is a portion of thedome-shaped surface 54 of FIGS. 7-9. The upper surface of first volume63 as pictured in FIG. 10 has a roughened surface and is not exactlyplanar, but that is slightly higher than the planar upper surfaceportion of die 58 in places, and extends down to the level of the planarupper surface portion of die 58 where the first volume makes contactwith die 58.

FIG. 11 is a cross-sectional view of the section of FIG. 10. There issubstantially no red-emitting phosphor within the volume of prism 66,nor is there substantially any red-emitting phosphor directly above die58. The second volume 64 contains substantially no red-emittingphosphor, rather substantially all of the red-emitting phosphor isdisposed in the first volume 63 so that the first luminescent material(including red-emitting phosphor) surrounds die 58 in a lateraldimension. The first volume makes contact with the upper surface 61 ofsubstrate 52 and also makes contact with the peripheral sides of theblue LED dice, including die 58.

FIG. 12 is a simplified top-down diagram of the section of FIG. 10. Thefour planes 71, 73, 75 and 77 of the four corresponding side faces 67,68, 69, and 70 of prism 66 are shown, as are the four peripheral sides72, 74, 76 and 78 of die 58.

FIG. 13 is a diagram that shows the ranges of wavelengths that areconsidered to be red light, orange light, yellow light, and green light,in one example. The first phosphor material of the first luminescentmaterial of the first volume 63 has an emission peak wavelength longerthan 620 nm. The second phosphor material (the second phosphor materialis actually a mixture of two phosphors) of the second luminescentmaterial of the second volume has peak emission wavelengths shorter than620 nm.

FIG. 14 is a table that illustrates an exemplary system of phosphors forthe white LED assembly 50 of FIG. 7. The first phosphor material is thephosphor set forth in the bottom row of the table. The second phosphormaterial is a mixture of the phosphors set forth in the upper two rowsof the table.

FIG. 15 is a simplified cross-sectional diagram of the section of FIG.10. A phosphor may be described to have a conversion efficiency inconverting the energy of absorbed light into the energy of re-emittedlight. Luminescence is very complex. There are different excitation andenergy transfer and luminescence mechanisms that affect conversionefficiency, but generally speaking for the types of phosphors used inhigh power LEDs, the stokes shift mainly dominates, and thereforeeffectively determines, the conversion efficiency of the phosphor.Accordingly, for one photon of blue light absorbed for one correspondingphoton of wavelength-shifted light emitted, a red-emitting phosphor willgenerate more heat than a yellow/orange-emitting phosphor or agreen-emitting phosphor. This is true even thought the quantumefficiency of the phosphor may be very close to one hundred percent.

In accordance with one novel aspect, the relatively less-efficientred-phosphor is disposed relatively close to the heat-sinking substrate52. None of the less-efficient, and therefore heat producing,red-emitting phosphor is disposed directly above die 58 where suchphosphor would contribute to increasing the temperature at the surfaceof die 58. Placement of the red-emitting phosphor (the first phosphormaterial) adjacent die 58 and in close proximity to the upper surface ofthe substrate 58, and not on top of die 58, allows thermal energygenerated in the relatively less efficient red-emitting phosphor to bemore effectively transported to the heat-sinking substrate 58 ascompared to the prior art structures of FIGS. 1-6, while simultaneouslyreducing the likelihood that red-emitting phosphor will interabsorblight emitted from yellow/orange-emitting phosphor and/or green-emittingphosphor of the LED assembly. Red light is of a lower energy than isyellow light, orange light and green light. Red light is not of adequateenergy to excite the yellow/orange-emitting and green-emittingphosphors. Consequently, most of the red light emitted from thered-emitting phosphor of the first volume 63 will pass through theyellow/orange-emitting and green-emitting phosphors of the second volume64 and out of the white LED assembly 50 without being absorbed. Due tothe placement of first volume 63, only a relatively small amount of theyellow/orange and green light emitted by phosphor particles of secondvolume 64 will travel back down and into the first volume 63.

In some cases, approximately ninety percent of the blue light emitted bydie 58 is emitted through the upper surface of the die, whereas aboutten percent of the blue light emitted by die 58 is emitted laterally outof the sides of die 58 at the approximate level of the InGaN/GaNMultiple Quantum Well active region 79 of die 58. In the presentembodiment, the concentration of red-emitting phosphor particles infirst volume 63 is higher than is the concentration ofyellow/orange-emitting phosphor and green-emitting phosphor in secondvolume 64. The relative concentrations of phosphors in the first andsecond volumes are set such that the composite light emitted from theupper surface of the overall white LED assembly 50 has the desired colortemperature.

FIG. 16 is a cross-sectional side view of a second white LED assembly100 in accordance with another novel aspect. A first contiguous volume101 of the first luminescent material surrounds dice 102 and 103 in thelateral dimension. None of the red-phosphor of the first volume isdisposed directly above a blue LED die. A second contiguous volume 104of the second luminescent material is disposed over the dice and overthe first volume as illustrated to form a dome-shaped lens structure.The substrate 105 is a Metal Core Printed Circuit Board (MCPCB)involving a thick metal substrate layer 106, an insulating layer 107,thin metal conductors 108, 109 and 110, a solder mask layer 111, ahighly reflective layer 112, and a retaining ring 113. Referencenumerals 114, 115 and 116 identify wire bonds.

FIG. 17 is a cross-sectional side view of a third white LED assembly 200in accordance with another novel aspect. The substrate 201 is a MCPCBsimilar to the MCPCB of FIG. 16, except that the dice 102 and 103 aredisposed in a reflector cup portion of the MCPCB. The reflector cup isthe depression illustrated in FIG. 17 that extends downward into theupper surface of substrate 201. The inner sidewall surface of thisreflector cup is lined with the highly reflective layer 112.

FIG. 18 is a cross-sectional side view of a fourth white LED assembly300 in accordance with another novel aspect. An amount 301 oftransparent silicone that includes little or no phosphor particles isdisposed over the first volume 63. The amount 301 of transparentsilicone is molded for form a plurality of mini-lens structures. A thinlayer 302 of a luminescent material involving yellow/orange-emittingphosphor particles (and few or no red-emitting phosphor particles, andfew or no green-emitting phosphor particles) is disposed over thetransparent silicone layer as illustrated. A thin layer 303 of aluminescent material involving green-emitting phosphor particles (andfew or no yellow/orange-emitting phosphor particles and few or nored-emitting phosphor particles) is disposed over layer 302 asillustrated.

FIG. 19 is a cross-sectional side view of a fifth white LED assembly 400in accordance with another novel aspect. The structure of FIG. 19 issimilar to the structure of FIG. 8, except that in the structure of FIG.19 the level of the upper surface of the first volume 63 is below thelevel of the substantially planar upper surface portions of the blue LEDdice 57-60.

FIG. 20 is a cross-sectional side view of a sixth white LED assembly 500in accordance with another novel aspect. The structure of the blue LEDdice 57-60 and the substrate 62 is the same as in the structure of FIG.19. A first contiguous volume 501 of the first luminescent materialforms a plurality of dome-shaped lens structures over the dice 57-60.There is one such dome-shaped lens structure over each corresponding oneof the dice. The first luminescent material includes a phosphor materialor materials that emit light in a spectrum that has a peak wavelengthlonger than 620 nm. The first luminescent material includessubstantially no phosphor material that emits light in a spectrum thathas a peak wavelength shorter than 620 nm. A second contiguous volume502 of the second luminescent material forms a covering over the firstvolume 501 as illustrated. The second luminescent material includes oneor more phosphor materials that emit light in a spectrum that has a peakwavelength shorter than 620 nm. The second luminescent material includessubstantially no phosphor material that emits light in a spectrum thathas a peak wavelength longer than 620 nm.

FIG. 21 is a cross-sectional side view of a seventh white LED assembly600 in accordance with another novel aspect. The structure andcomposition of the assembly of FIG. 21 is the same as the structure andcomposition of the assembly of FIG. 20, except that the upper surface ofthe first volume 501 in the structure of FIG. 21 forms many more andsmaller dome-shaped lens structures. The dome-shaped structures are notprovided to focus light, but rather are provided to facilitate lightescaping from the first volume 501 and propagating into the secondvolume 502.

FIG. 22 is a cross-sectional side view of an eighth white LED assembly700 in accordance with another novel aspect. In this assembly, thinportions of the first volume 63 extend over and cover the blue LED dice57-60. The thin portions are half a millimeter of less in thickness.First volume 63 extends down and contacts the upper surface of thesubstrate 52 in the areas around the dice. Second volume 64 is molded toform an array of dome-shaped mini-lens structures. There is one suchdome-shaped structure disposed over each corresponding respective one ofthe blue LED dice. Reference numerals 53-56 identify four of thesedome-shaped mini-lens structures.

FIG. 23 is a flowchart of a method 800 in accordance with one novelaspect. A blue LED die is attached (step 801) to a substrate such thatthe die defines a Right Rectangular Prism (RRP) having four side faces.The bottom surface of the die is planar and lies in a plane that iscoplanar with the bottom face of the RRP. A first peripheral side of thedie lies in a first plane that is coplanar with a first side face of theRRP. A second peripheral side of the die lies in a second plane that iscoplanar with a second side face of the RRP. A third peripheral side ofthe die lies in a third plane that is coplanar with a third side face ofthe RRP. A fourth peripheral side of the die lies in a fourth plane thatis coplanar with a fourth side face of the RRP. In one example, the RRPis a virtual prism as illustrated in FIG. 10.

A first volume of a first luminescent material is then formed (step 802)such that the first volume is disposed entirely outside the RRP, andsuch that the first volume surrounds the RRP in the lateral dimension.Substantially none of the first luminescent material is disposeddirectly above the die. The first luminescent material comprises a firstphosphor material capable of emitting light having a first peakwavelength longer than 620 nm, and comprises substantially no phosphormaterial capable of emitting light having a peak wavelength shorter thanapproximately 620 nm.

In one example, the first volume is formed by jetting microdots of thefirst luminescent material onto the substrate around the dice in anuncured state. Each microdot is less than 100 microns in diameter.Silicone of the first luminescent material is then allowed to cure andharden. In another example, the first volume is formed by screenprinting the first luminescent material onto the substrate around thedice in an uncured state, and then allowing silicone of the firstluminescent material to cure and harden. In one example of method 800,substantially all phosphor particles in the first volume are the samephosphor and have the same absorption and emission characteristics. Inanother example of method 800, the phosphor particles in the firstvolume are a mixture of multiple different types of phosphors and havemultiple different absorption and emission characteristics. The firstvolume of method 800 is, however, a single contiguous amount of thefirst luminescent material that extends around and contacts each LED dieof the assembly. In one example the first volume of method 800 is thefirst volume 63 of the white LED assembly 50 illustrated and explainedin connection with FIGS. 7-15.

A second volume of a second luminescent material is then formed (step803) such that the second volume is disposed at least in part above thedie within the RRP. The second luminescent material comprises a secondphosphor material capable of emitting light having a second peakwavelength shorter than 620 nm, and comprises substantially no phosphormaterial capable of emitting light having a peak wavelength longer thanapproximately 620 nm. In one example the second volume is the secondvolume 64 of the white LED assembly 50 illustrated and explained inconnection with FIGS. 7-15. In one example of method 800, substantiallyall phosphor particles in the second volume are the same phosphor andhave the same absorption and emission characteristics. In anotherexample of method 800, the phosphor particles in the second volume are amixture of multiple different types of phosphors and have multipledifferent absorption and emission characteristics. The second volume ofmethod 800 is, however, a single contiguous amount of the secondluminescent material that extends over and covers all the LED dice ofthe assembly.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A Light Emitting Diode (LED) assembly comprising:a substrate; a LED die disposed on the substrate, wherein the LED diedefines a right rectangular prism (RRP) having four side faces, whereina first peripheral side of the LED die lies in a first plane that issubstantially coplanar with a first side face of the RRP, wherein asecond peripheral side of the LED die lies in a second plane that issubstantially coplanar with a second side face of the RRP, wherein athird peripheral side of the LED die lies in a third plane that issubstantially coplanar with a third side face of the RRP, wherein afourth peripheral side of the LED die lies in a fourth plane that issubstantially coplanar with a fourth side face of the RRP; a firstvolume of a first luminescent material that is disposed entirely outsidethe RRP, wherein the first volume surrounds the RRP in a lateraldimension, wherein the first luminescent material comprises a firstphosphor material capable of emitting light having a first peakwavelength longer than 620 nanometers, wherein the first volumecomprises substantially no phosphor material capable of emitting lighthaving a peak wavelength shorter than approximately 620 nanometers; anda second volume of a second luminescent material that is disposed atleast in part above the LED die within the RRP, wherein the secondluminescent material comprises a second phosphor material capable ofemitting light having a second peak wavelength shorter than 620nanometers, wherein the second volume comprises substantially nophosphor material capable of emitting light having a peak wavelengthlonger than approximately 620 nanometers.
 2. The LED assembly of claim1, wherein a first portion of the second volume of the secondluminescent material is disposed outside the RRP, wherein a secondportion of the second volume of the second luminescent material isdisposed within the RRP and extends across an upper surface of the LEDdie, wherein the first and second portions of the second volume form alayer, and wherein the layer has a substantially uniform thickness. 3.The LED assembly of claim 1, wherein the LED has a substantially planar(means it can be patterned for light emission improvement) upper surfaceportion that extends in a plane, and wherein the first volume ofluminescent material is disposed entirely between the plane of the uppersurface portion and the substrate.
 4. The LED assembly of claim 1,wherein the first volume of the first luminescent material contacts anupper surface of the substrate, and wherein the first volume of thefirst luminescent material contacts the first, second, third and fourthperipheral sides of the LED die.
 5. The LED assembly of claim 1, whereinthe first luminescent material comprises the first phosphor material anda material taken from the group consisting of: silicone, resin andepoxy, and wherein the second luminescent material comprises the secondphosphor material and a material taken from the group consisting of:silicone, resin and epoxy.
 6. The LED assembly of claim 1, wherein thefirst volume is substantially free of the second phosphor material, andwherein the second volume is substantially free of the first phosphormaterial.
 7. The LED assembly of claim 1, wherein the first volumecomprises an amount of red-emitting phosphor particles, and wherein thesecond volume contains substantially no red-emitting phosphor particles.8. The LED assembly of claim 1, wherein the first volume has asubstantially planar upper surface, wherein the LED die has asubstantially planar upper surface portion, and wherein thesubstantially planar upper surface of the first volume is parallel tothe substantially planar upper surface portion of the LED die.
 9. TheLED assembly of claim 1, further comprising: a lens disposed between thefirst volume and the second volume, wherein the lens is substantiallyfree of phosphor particles.
 10. The LED assembly of claim 9, wherein thelens has a dome-shaped surface, and wherein the second volume of thesecond luminescent material is a layer of substantially uniformthickness that extends over and covers the dome-shaped surface.
 11. TheLED assembly of claim 1, further comprising: a structure disposedbetween the first volume and the second volume, wherein the structurehas a dome-shaped surface, and wherein the structure is substantiallyfree of phosphor particles.
 12. The LED assembly of claim 1, wherein thesubstrate is a metal core printed circuit board, and wherein the LED dieis taken from the group consisting of: a vertically-contacted LED die, alaterally-contacted LED die, a blue LED, and a UV-emitting LED.
 13. TheLED assembly of claim 1, wherein the substrate has a substantiallyplanar surface portion and a reflector cup portion.
 14. A Light EmittingDiode (LED) assembly comprising: a substrate; a LED die disposed on thesubstrate; a first volume of a first luminescent material that surroundsthe LED die in a lateral dimension, wherein no part of the first volumeis disposed directly above any part of the LED die, wherein the firstluminescent material comprises a first phosphor material capable ofemitting light having a first peak wavelength longer than 620nanometers, wherein the first volume comprises substantially no phosphormaterial capable of emitting light having a peak wavelength shorter thanapproximately 620 nanometers; and a second volume of a secondluminescent material that is disposed at least in part directly abovethe LED die, wherein the second luminescent material comprises a secondphosphor material capable of emitting light having a second peakwavelength shorter than 620 nanometers, wherein the second volumecomprises substantially no phosphor material capable of emitting lighthaving a peak wavelength longer than approximately 620 nanometers. 15.The LED assembly of claim 14, wherein the second volume is a layer ofsubstantially uniform thickness, and wherein the layer extends over andcovers the LED die.
 16. The LED assembly of claim 15, wherein the layerdoes not contact the LED die.
 17. The LED assembly of claim 15, whereinthe layer contacts the LED die.
 18. A method of manufacturing an LEDassembly, wherein the LED assembly comprises an LED die disposed on asubstrate, wherein the LED die defines a right rectangular prism (RRP)having four side faces, a first peripheral side of the LED die lies in afirst plane that is substantially coplanar with a first side face of theRRP, a second peripheral side of the LED die lies in a second plane thatis substantially coplanar with a second side face of the RRP, a thirdperipheral side of the LED die lies in a third plane that issubstantially coplanar with a third side face of the RRP, a fourthperipheral side of the LED die lies in a fourth plane that issubstantially coplanar with a fourth side face of the RRP, the method ofmanufacturing comprising: (a) forming a first volume of a firstluminescent material such that the first volume is disposed entirelyoutside the RRP and such that the first volume surrounds the RRP in alateral dimension, wherein the first luminescent material comprises afirst phosphor material capable of emitting light having a first peakwavelength longer than 620 nanometers, wherein the first volumecomprises substantially no phosphor material capable of emitting lighthaving a peak wavelength shorter than approximately 620 nanometers; and(b) forming a second volume of a second luminescent material that isdisposed at least in part above the LED die within the RRP, wherein thesecond luminescent material comprises a second phosphor material capableof emitting light having a second peak wavelength shorter than 620nanometers, wherein the second volume comprises substantially nophosphor material capable of emitting light having a peak wavelengthlonger than approximately 620 nanometers.
 19. The method of claim 18,wherein the forming of (a) involves jetting microdots of the firstluminescent material such that the first volume contacts the substrateand contacts the LED die, wherein each microdot is less than 100 micronsin diameter.
 20. The method of claim 18, wherein the forming of (b)involves forming the second volume such that the second volume has oneor more dome-shaped portions.